1) Field of the Invention
The present invention relates to an inverter device capable of reducing through current generated when two series connected switching elements that are on/off controlled.
2) Description of the Related Art
An inverter device is used as, for example, a driving device for a three-phase motor. The inverter device used as the three-phase motor driving device includes an output circuit. This output circuit includes pairs of switching elements to which fly-wheel diodes are connected, respectively, in series between the positive electrode terminal and the negative electrode terminal (ground terminal) of a direct-current (DC) power supply and the pairs of switching elements are connected in parallel for the three phases. An output to a motor is fetched from the connection end between each pair of switching elements connected in series (see, for example, Kuniaki Makabe, Control Circuit Design for Stepping Motor, (CQ Publishing Co., Ltd., pp. 35 to 118)).
The output circuit of the inverter device is controlled according to pulse width modulation (PWM) method. Namely, the output circuit is controlled so that each of pairs of switching elements connected in series are alternately turned on and off, the ON/OFF operation time ratio of the pair is changed to thereby change the magnitudes of the output voltages thereof, and that the combinations of the pairs turned on and off are changed to change the polarities of the output voltages.
Each pair of switching elements connected in series is controlled to be alternately turned on and off with OFF operation periods given to the operations of the pair so that the ON operation states of the pair do not occur concurrently. During this time, a motor driving current in each phase is carried without intermission. That is, if the operation of one of the switching elements of, for example, an upper arm is switched from an ON operation state to an OFF operation state, the corresponding one of the switching elements of a lower arm is in an OFF operation state.
However, a regenerative current generated by the energy accumulated by the inductance of the motor flows, while being attenuated, in the same direction as the motor driving current is carried to the fly-wheel diode connected to the switching element of the upper arm. The switching element of the lower arm is then turned on, and the motor driving current in the same direction is carried to the switching element of the lower arm. The fly-wheel diode of the upper arm is applied with a backward voltage and turned off.
The conventional technology has the following disadvantages. During the operation process, when the fly-wheel diode of the upper arm is turned off in response to the ON operation of the switching element of the lower arm, a backward current (backward recovery current) is carried to the fly-wheel diode of the upper arm for the time that is specified by backward recovery characteristic of the diode. For that reason, a short-circuit between the positive electrode terminal and the negative electrode terminal of the DC power supply occurs, though momentarily, in which, a through current flows. This backward recovery current carried to the fly-wheel diode of the upper arm becomes excessive if the switching speed of the switching element of the lower arm is high, thereby disadvantageously making circuit operation unstable.
It is an object of the present invention to solve at least the problems in the conventional technology.
The inverter device according to one aspect of the present invention comprises a direct-current power supply having a positive electrode terminal and a negative electrode terminal; a first set of switching elements including a plurality of switching elements connected in parallel; a second set of switching elements including a plurality of switching elements connected in parallel, wherein each of the switching elements of the first set being connected in series with a corresponding one of the switching elements of the second set to form a pair of switching elements including a first switching element and a second switching element, between the positive electrode terminal and the negative electrode terminal of the direct-current power supply; a plurality of fly-wheel diodes, each of the fly-wheel diodes being connected to each of the first switching element and the second switching element, wherein the first switching element and the second switching element being turned on and off alternately while changing a time ratio and a signal output at a node between the first switching element and the second switching element being supplied to an inductance load; a first transistor that receives a control signal for turning on the first switching element, applies a power supply voltage to a control electrode of first switching element, and starts charging a miller capacitance of the first switching element; a detection circuit that detects a timing at which a voltage of the control electrode of the first switching element reaches a logic inversion voltage while the control signal for turning on the first switching element, and outputs a detection signal indicating the timing; and a second transistor that receives the detection signal, applies the power supply voltage to the control electrode of the first switching element, and accelerates charging the miller capacitance.
The inverter device according to another aspect of the present invention includes a direct-current power supply having a positive electrode terminal and a negative electrode terminal; a first set of switching elements including a plurality of switching elements connected in parallel; a second set of switching elements including a plurality of switching elements connected in parallel, wherein each of the switching elements of the first set being connected in series with a corresponding one of the switching elements of the second set to form a pair of switching elements including a first switching element and a second switching element, between the positive electrode terminal and the negative electrode terminal of the direct-current power supply; a plurality of fly-wheel diodes, each of the fly-wheel diodes being connected to each of the first switching element and the second switching element, wherein the first switching element and the second switching element being turned on and off alternately while changing a time ratio and a signal output at a node between the first switching element and the second switching element being supplied to an inductance load; a first transistor that receives a control signal for turning on the first switching element, applies a power supply voltage to a control electrode of first switching element, and starts charging a miller capacitance of the first switching element; a detection circuit that detects a timing at which a potential difference between both signal electrodes of the first switching element reaches a logic inversion voltage while the control signal for turning on the first switching element, and outputs a detection signal indicating the timing; and a second transistor that receives the detection signal, applies the power supply voltage to the control electrode of the first switching element, and accelerates charging the miller capacitance.
The other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed descriptions of the invention when read in conjunction with the accompanying drawings.